This invention relates to a unique swim fin that differs considerably from swim fins of the prior art in its basic concept of and in the configuration of the boot into a flexible "Fish body" (boot/body) with a stiff caudal fin or tail (tail/blade) that act as a wing in producing "Lift" as a form of propulsion. This "Fish body" type of structure also allows for modular construction and great flexibility in the combining of different tail/blades to flexible boot/bodies to adapt to the different swimming conditions, styles, and body types of swimmers. This invention specifically improves the method of propulsion from one of resistance to one of "lift" propulsion, it improves the fluid dynamic flow of water to increase "still" water contact and therefore efficiency, it improves the bio-mechanical relationship to natural human kicking motions, it improves the propulsion phase of the fin from a power/recovery cycle to a power/power cycle, it improves the propulsion by employing a recoil memory material in the flexible body/boot that delivers a rebound kick at the change of direction in kicking.